1. Field of the Invention
The invention relates to a device for palletizing parcels, preferably stacks of tubular sections or flat lying sacks. Said device comprises a lifting frame, which can be raised and lowered in a stand and which is provided with a guide, slide or transport track, preferably a roller track, in order to slide the pallets on and off. Said device also comprises a conveyor, which supplies the parcels to be stacked and from which a controlled transfer unit takes the supplied parcels and deposits them on a pallet, provided on the guide, slide or transport track.
2. Description of the Related Art
For example, in the manufacture of sacks tubular sections, which are processed by molding the bottoms to the sacks, must usually be put into intermediate storage, because the tube drawing machines, producing the tubular sections, work at a significantly higher speed than the systems, processing the tubular sections into sacks. Such an intermediate storage is usually achieved by stacking the tubular sections into stacks, containing a predetermined number of items, and then depositing the stacks on manipulatable pallets. Furthermore, the manufactured sacks must usually also be stacked and the stacks must be deposited on pallets, in order to store or transport them.
In the known class of devices for palletizing, as described in the introductory part of the specification, there is the problem that the pallets, which receive the parcels and on which the parcels are deposited in multiple layers with straight edges, according to a specified pattern in accordance with the programmed control unit of the transfer gripper, are not aligned accurately in relation to the transfer gripper, so that the parcels are stacked into stacks that are offset or skewed on the pallet. This state can lead to problems during the conveying and storage sequence, because the stacks project beyond the side edges of the pallet.
Therefore, the object of the invention is to provide a device of the aforementioned class that guarantees that the pallets are always accurately aligned relative to the transfer gripper, so that it deposits the parcels to be palletized with positioning accuracy in several layers on the pallet.
The invention solves this problem associated with a device of the aforementioned class in that above the conveying plane of the guide, slide or transport track there are stops or clamping elements that can be moved in the opposing direction in the lifting frame and which act on the opposing sides or comers of the pallet and fix them in a position, in which the transfer unit deposits the parcels with positioning accuracy, according to the predetermined pattern, on the pallet.
In the device, according to the invention, the stops or the clamping elements, which can be moved in opposing directions, align the pallet in a predetermined position on the lifting frame and fix it in this position, whereby the stops can also act like clamping elements on the sides of the pallets with slight pressure and thus clamp the pallets in position. However, clamping is not necessary, since the stops can move the pallet into its correct position and hold it there even without the clamping effect. To prevent that the stops or clamping elements, which act on the opposing sides of the pallet, prevent the pallet from being moved into the aligned end position, the clamping forces of the stops or the clamping strips can be coordinated in such a manner that a pair of stops or clamping elements act only with less force on the pallet and the two other stops and clamping elements can shift the pallet into the aligned end position due to their greater force. When the pallet is accurately aligned on the lifting frame by means of the stops or clamping elements, the transfer gripper, which can be controlled by a computer, can deposit the parcels in layers, according to a predetermined pattern, in such a manner on the pallet that the palletized stacks exhibit straight edges and do not project beyond the pallets.
A further development of the invention provides that on both sides of the lifting frame are mounted four chain wheels around axles, running at right angles to the slide on and slide off direction of the pallets, so as to be mirror images in relation to the transversal central plane of the lifting frame. Two continuous chains run on each side of the chain wheels. Clamping or stop elements are fastened to the opposing chains at right angles to the conveying direction. The chains are provided in such a manner with drives that they traverse the clamping elements in opposing directions. The clamping elements are coordinated in such a manner that in their joined position they fix the pallet to be loaded between them in a position, in which it is in alignment with the accepting gripper in the conveying direction. The drives of the chains are only so strong that they come to a standstill, when the pallet is moved by the stop elements into a position, in which they rest on the front and rear side of the pallet.
To guarantee that the clamping or stop elements will move synchronously, the shafts of the inside chain wheels can be coupled together by means of gearwheels.
Preferably a pressure medium piston cylinder unit acts as the drive on a chain.
To align also the pallet, slid on the lifting frame, at right angles to the conveying direction, a further development of the invention provides that on both sides of the lifting frame are mounted chain wheels around axles, pointing in the conveying direction. Two continuous chains run over said chain wheels; and the stops or clamping elements, which run parallel to each other over holders, are fastened to the upper strands and the lower strands of the chains. Said stops or clamping elements can be moved stops or clamping elements in opposite directions by driving the chains synchronously. Even this drive is formed only so strong that it comes to a standstill when the stops or clamping elements rest on both sides of the pallet.
Expediently the sliders are guided by guide elements, for example sleeves, on a traverse that runs at right angles to said sleeves.
To drive the chains, there is a pressure medium piston cylinder unit, whose piston rod is fastened to a slider and whose cylinder is fastened to the lifting frame. Expediently the pressure medium cylinder unit comprises pneumatic cylinders.
Preferably the lifting frame is provided with driven rollers so that the pallets can be accepted by the lifting frame by suitably controlling the drive.